The present invention relates to a method for improving call processing in a number portability environment. Specifically, the present invention relates to a method for reducing post-dial delay while routing calls in a number portability context.
The U.S. telecommunications network is in a state of transition. In the not too distant future it is expected that the monopoly held by local exchange carriers will be substantially altered and that Competitive Access Providers (CAPS) will begin to provide competitive provide local exchange service. To accomplish this without creating an excessive burden on customers who wish to receive service from a CAP, the customers will be able to change to a CAP without requiring the change of a telephone number. This type of flexibility is referred to as service provider number portability. It enables the subscriber to change his or her service provider while maintaining the same directory number. The public policy goal is to ensure that there is no performance degradation between carriers.
It is also expected that subscribers will be able to move between geographic locations within some reasonably defined region, for example, within the same LATA, while retaining the same telephone number. This is referred to as geographic portability. In this case the subscriber may or may not change service providers.
An additional type of portability relates to a customer's desire to change the type of service in use. For instance, a customer may change from Plain Old Telephone Service (POTS) to IDSN service and wish to maintain the same directory number. This is referred to as service portability.
AT&T has already proposed a system for providing both service provider and geographic number portability. This system uses a mechanism referred to as the Location Routing Number (LRN) mechanism. In the Location Routing Number mechanism during call processing a local switch analyzes the dialed number to determine both whether that number is from a portable NPA-NXX, that is, whether at least one NPA-NXX-XXXX has ported to another local switch, and whether the call is interswitch, that is whether or not a different local switch serves the destination number. If the number's NPA-NXX is determined to be portable and if the call is interswitch then the network switch launches a query to a number portability (NP) database. If the number has been ported the database then returns a location routing number (LRN) of the recipient switch to which the dialed number has been ported. The querying switch receives the LRN and uses it to route the call to its correct destination.
If the number has not been ported then the NP database returns the dialed number (DN) and the switch appropriately routes the call.
Examples of the call flow in the LRN mechanism are illustrated in prior art FIGS. 1 and 2.
FIG. 1 illustrates call processing in an LRN mechanism when a call from a calling party A to a called party B is a local interswitch call. In the example, in step 1 party A (having number 212-949-3001) dials 212-984-3001, the number assigned to party B. The end office (EO) 10 of local service provider (LSP) 1 receives the dialed number and determines that the number's NPA-NXX is portable. EO 10 then launches a query via Signaling Transfer Point (STP) 20 to a number portability (NP) database 30. The query includes the dialed number received by EO 10. The NP database 30 then returns the location routing number to the EO 10. The first six digits of the LRN are indicative of a particular LSP EO. The LRN is populated in the Called Party Number ISUP (ISDN user port) parameter of the Initial Address Message (IAM) of the Signaling System 7 (SS7) protocol. The dialed number is placed in the generic address parameter (GAP). Furthermore, an indicator is set to represent the fact that the routing information is based on a query to the database. When the EO 10 receives this information it then routes the call to the tandem switch 40 based on the first six digits of the LRN. The tandem switch then routes the call to the end office of the LSP 3, 50, to which called party B is presently ported rather than the end office of LSP 2, 60, to which the called party B was previously ported. Finally, in a fifth step the EO 50 presently serving the ported subscriber recognizes its own LRN and obtains the dialed number from the generic address parameter and uses that information to complete the call to station B. In summary, for interswitch calls to portable NPA-NXXs the end office switch 10 launches a query to a database to obtain routing information for the end office which is servicing the ported customer.
FIG. 2 illustrates a similar situation in the context of an interLATA call where the call must be serviced by an Inter-Exchange Carrier (IXC). Like elements in FIGS. 1 and 2 bear identical reference numerals. In this instance the EO 10 determines that the call is an interLATA call and therefore sends the dialed number information to the IXC originating switch 15. The IXC recognizes the dialed number as pertaining to a portable NPA-NXX and generates a query using the dialed number (212-984-3001 in the illustrated example). The query goes to the Signaling Transfer Point (STP) 25 and is forwarded to a number portability (NP) database 35. The NP database 35 could be a national universal database. The distinctions between the database 35 of FIG. 2 and the database 30 of FIG. 1 could correspond to the differences between the national and local databases described in co-pending application serial no. 08/861,755, the entire disclosure of which is incorporated by reference hereto. As in the case of the query response in FIG. 1, if the number has been ported, the NP database 35 provides the LRN information associated with the dialed number. The originating IXC switch formats an ISUP IAM and places the LRN information (here 212-484-9999) in the called party number parameter. The dialed number is stored in the generic address parameter and the M-bit of the Forward Call indicator (FCI) is set to indicate that the NP database 35 was queried. The originating IXC 15 then routes the call to terminating IXC switch 45 based on the first six digits of the LRN. The terminating IXC switch determines a routing path to the EO 55 of LSP 3, 50, based on the first six digits of the LRN. The end office 55 recognizes its own LRN and then obtains the dialed number from the GAP and completes the call to station B.
In the two examples described, a query is launched to the database, either local database 30 or national database 35 each time an interswitch call to a portable NPA-NXX is detected. As a result, the system generates a large number of queries. In fact, for a frequently dialed number a query related to that dialed number may have been processed only a few minutes or even perhaps just a few seconds, earlier. These queries come at a cost. First, there is the load on the system in query traffic. Then there is the processing to be done at the NP database to respond to all queries. Finally, there is a built-in delay for processing all interswitch calls to portable NPA-NXXs since a query must be launched and processed before the call is routed. In a co-pending application by the same inventors filed on the same date as the present application it is proposed to employ a cache at the switching office that launches the database query. The cache is checked before a query is launched so that if LRN response information is in the cache there is no query unless upon attempting a connection using the LRN response information in the cache the attempt fails because the cached information is incorrect. That deployment of a cache reduces queries. However, the inventors have also noted that post-dial delay, a phenomenon of concern to service providers, can be exacerbated by delaying the launch of database queries until an attempt to connect using cached LRN response information fails. The communication industry has recognized that the delay experienced by a calling party after completing the dialing of a number can have a significant impact on the perception of the service provided. Too long a delay may present a very clear indication that the called party is now ported to a different service provider and may suggest that there is a degradation of service as a result of the porting. There is no agreement within the industry regarding acceptable values for post-dial delay. It would therefore be beneficial to reduce post-dial delay wherever possible to avoid the appearance of service degradation to the calling party.